linux-kernel - Re: [PATCH 2/2] thermal: tegra-bpmp: Always (re)program trip temperatures

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Date:   Wed, 8 Feb 2023 11:43:04 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Mikko Perttunen <cyndis@...si.fi>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Srikar Srimath Tirumala <srikars@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Timo Alho <talho@...dia.com>, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] thermal: tegra-bpmp: Always (re)program trip
 temperatures

On Tue, Feb 07, 2023 at 03:56:09PM +0200, Mikko Perttunen wrote:
> From: Mikko Perttunen <mperttunen@...dia.com>
> 
> In the rare case that calculation of trip temperatures would result
> in the same trip temperatures that were previously programmed, the
> thermal core skips calling .set_trips.

That seems like an appropriate optimization.

> However, presently, if it is not called, we may end up with no trip
> temperatures programmed at all.

I have a hard time understanding when this would happen. prev_low_trip
and prev_high_trip are -INT_MAX and INT_MAX, respectively, so these are
unlikely to be the result of anything we compute at runtime, based on
temperatures specified in DT, for example.

So I would expect ->set_trips() to get called at least once when the
thermal zones are first registered. Are you saying there are cases where
->set_trips() doesn't get called at all?

> To avoid this, make set_trips a no-op and in places where it would be
> called, instead unconditionally program trip temperatures to the last
> specified temperatures.

Again, this seems more like a workaround for an issue that exists
elsewhere. If ->set_trips() doesn't always get called when it should be,
then that's what we should fix.

> This also fixes the situation where a trip is triggered between
> registering a thermal zone and registering the trip MRQ handler, in
> which case we would also get stuck.

Could this be fixed by requesting the MRQ prior to registering the
zones? That seems like the more appropriate fix for this issue. It's
similar to how we typically register IRQ handlers before enabling a
device to make sure we don't miss any interrupts.

Thierry

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